Preparation And Performance Study Of Nano-SiC Reinforced Cu-based Powder Metallurgy Friction Materials

Cu-based powder matellurgy(PM) friction material is one of the widest used brake pad materials of automobile and high-speed train in the world, it has many advantages which cannot be substituted by traditional phenolic-based friction material, such as excellent heat resistance, high mechanical strength, stable friction and wear performances, et. al. For friction materials applied in high speed, heavy load, or high temperature circumstances, working circumstance of friction materials is increasingly harsh, which sets higher standards for mechanical strength and stability of friction materials. At present, two hotspots of researchs on improving performances of PM friction material are: 1. Formulation optimization; 2. Preparation technique optimization.In this thesis, Cu-based PM friction materials reinforced by nano-SiC particles(n-SiC) are prepared by technique of “cold pressing moulding-hot pressing sintering” under four different sintering temperatures, the best sintering temperature is selected by comparing the microscopic structure and physical-mechanical properties of sintered samples. Cu-based PM friction materials with different content of nano-SiC particles are prepared under the best sintering temperature, microscopic structure, physical-mechanical properties and friction and wear performance are studied. The results show that:1.Sintering temperature significantly influences the microscopic structure and physical and mechanical properties of PM friction materials. With the rising of sintering temperature from 810℃ to 850℃, the amount of pores in the surface decreases evidently, intergration of Cu matrix improves with interfaces between different components lessening, thus density of PM friction materials enhances while porosity decreases, hardness increases significantly. When sintering temperature comes to 870℃, microscopic structure of the sample changes little, while both density and hardness decrease. 2. Cu-based PM friction materials with different contents of nano-SiC particles are prepared under 850℃. With the increase of n-SiC particles content, hardness of PM friction materials increases at first and then decreases, it reaches maximum when 1wt% of n-SiC particles are added, which means the achievement of best reinforcement effect. When the addition of n-SiC particles exceeds 1%, agglomerations of nano particles appearance, hardness of the sample with 4%n-SiC is the lowest. 3. Results of tests on friction and wear performances of PM friction materials with different content of n-SiC particles show that: when rotate speed and pressure are low, with the increase of n-SiC particles content, friction coefficient(COF) increases at first and then decreases, weight loss increases slowly, the sample with 1%n-SiC has the highest COF, the wear mechanism under this situation is abrasive wear; when rotate speed is low and pressure is high, with the increase of n-SiC particles content, COF decreases at first and then increases, weight loss decreases at first and then increases, the sample with 0.5%n-SiC has the lowest COF and samples with 0.5%~1%n-SiC have the lowest weight loss, the wear mechanism under this situation are abrasive wear and slight adhesive wear; when rotate speed is high, under different pressures, with the increase of n-SiC particles content, both COF and weight loss decrease at first and then increase, sample with 1%n-SiC has the lowest COF and weight loss at high pressure, while the sample without n-SiC particles is wore severly, under high speed low pressure, the wear mechanism is fatigue wear, under high speed and high pressure, the wear mechanism are delaminate wear and fatigue wear. In conclusion, adding 1% n-SiC particles into Cu-based PM friction material improves the stablility of COF and wear resistant property at high speed and high pressure circumstance.